1. Field of the Invention
The present invention relates generally to methods for fabricating three-dimensional objects. More specifically, the present invention relates to a method for fabricating three-dimensional objects in incremental layers employing data generated in a CAD/CAM system, the method steps being controlled by a central computer or distributed data processing system.
2. Background Information
Recently, there have been great strides in technology relating to rapid prototyping and manufacturing ("RP&M"), particularly to the integration of CAD/CAM ("Computer Aided Design/Computer Aided Manufacturing") systems into the object fabrication process beyond simple object design and drafting. A goal of this technology is to obtain a final or near-final three-dimensional object or part from CAD/CAM data with as little human intervention as possible. A comprehensive discussion of the state of the RP&M art is found in Rapid Prototyping and Manufacturing, P. Jacobs et al. (Society of Manufacturing Engineers, 1992). Another useful reference discussing the state of the art is found in Automated Fabrication: Improving Productivity in Manufacturing, M. Burns (PTR Prentice Hall, 1993).
One technology that has received a great deal of attention in this regard is known as "stereolithography," which literally means "three-dimensional printing." In stereolithography, dimensional data generated in a CAD/CAM system is employed to "print" an object in a fully or near-fully automated fabrication system. The most commercially successful stereolithography method and apparatus is disclosed in a number of patents assigned to 3-D Systems Inc. of Valencia, Calif. The 3-D Systems method and apparatus employs CAD/CAM data to control a beam of radiant energy (laser). The beam of radiant energy is directed into a bath of radiantly (ultra-violet) cured liquid polymer (photopolymer) to selectively cure the polymer and thus build an object through accumulation of incremental layers of cured polymer. Thus, the three-dimensional printing is accomplished by selective curing of substantially two-dimensional layers of polymeric material.
Another method and apparatus for RP&M is disclosed in a series of patents assigned to the University of Texas. In this method, a CAD/CAM system is employed to control a laser, which selectively sinters particles of material, typically a plastic powder, to form the object through accumulation of incremental layers of sintered material.
Other known RP&M systems adhesively laminate together layers of polymeric or paper tape. Each layer is trimmed by a laser or other means to the cross-sectional dimensions of the object, wherein accumulation of layers of tape forms the fully fabricated object. A generic term for all of these RP&M apparatus is "free-form" fabricators.
A drawback to all of these methods is that the ultimate part or object, while in some respects satisfactory for model building, generally lacks the material properties desired of a satisfactory prototype part. For example, the parts resulting from the cured liquid polymer processes tend to be brittle. The parts resulting from the laser sintering process suffer from the porosity and strength problems typical of sintered parts.
One attempted solution to this problem is disclosed in a series of patents assigned to the University of Southern California. In this process, liquid metal is deposited in droplet form and the droplet stream is manipulated to form the object through accumulation and solidification of the metal droplets. This process results in a satisfactory metallic prototype part or object, but is extremely complex, even in the context of this complex technological area, is extremely expensive, and the control systems are not sufficiently developed to accurately and repeatably produce prototype parts with satisfactory dimensional tolerances.
A further drawback to these methods is that they are time-consuming and expensive, typically costing several hundred thousand dollars at initial purchase price. Unwieldy (tape and vats of liquid or powdered polymer) and hazardous (ultraviolet-cured photopolymers) materials are used in several of these processes. Moreover, these RP&M methods require relatively large apparatus operating under controlled conditions. Nevertheless, the time and expense consumed by these RP&M methods is small compared to the time and cost necessary to produce a prototype part using conventional tooling and manufacturing processes.
The previously mentioned 3-D Systems Inc. has advanced the state of RP&M technology with its Actua 2100.TM. modeler. This system uses an "ink-jet" technology to deposit layers of a waxy polymer to build up a model. This system is faster than laser-driven photopolymer or sintering systems, has a smaller "footprint" than prior stereolithography apparatus, and costs less than one hundred thousand dollars. Nevertheless, because the Actua 2100.TM. is confined by the "ink-jet" process that it uses to waxy polymers, there is room for improvement in the material properties of the resulting part.
A need exists, therefore, for a method of fabricating objects, employing free-form fabricators, that produces a prototype part having satisfactory material properties in a shorter time interval and using a less bulky apparatus.